U.S. patent application number 13/144661 was filed with the patent office on 2011-11-10 for solvent removal and recovery from inorganic and organic solutions.
Invention is credited to Vinodkumar Ambalal Patel, Nandakishore Rajagopalan.
Application Number | 20110272355 13/144661 |
Document ID | / |
Family ID | 42396297 |
Filed Date | 2011-11-10 |
United States Patent
Application |
20110272355 |
Kind Code |
A1 |
Rajagopalan; Nandakishore ;
et al. |
November 10, 2011 |
SOLVENT REMOVAL AND RECOVERY FROM INORGANIC AND ORGANIC
SOLUTIONS
Abstract
A process for recovering solvents from inorganic and organic
solutions is disclosed. The process utilizes a polymer capable of
selectively extracting the solvent from the inorganic or organic
solution. Introduction of the polymer into the solvent solution
creates formation of a polymer-rich phase and a solute-rich phase.
The recovered solvent may be separated from the polymer-rich phase
by heating the polymer-rich phase to at least the cloud point of
the polymer. The polymer and/or solute may be re-cycled for further
use in the solvent recovery process.
Inventors: |
Rajagopalan; Nandakishore;
(Champaign, IL) ; Patel; Vinodkumar Ambalal;
(Urbana, IL) |
Family ID: |
42396297 |
Appl. No.: |
13/144661 |
Filed: |
January 25, 2010 |
PCT Filed: |
January 25, 2010 |
PCT NO: |
PCT/US10/21932 |
371 Date: |
July 14, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61148270 |
Jan 29, 2009 |
|
|
|
Current U.S.
Class: |
210/650 ;
210/670 |
Current CPC
Class: |
C02F 1/26 20130101; C02F
2103/08 20130101; B01D 11/0492 20130101; C02F 1/52 20130101; C02F
1/02 20130101; C02F 1/441 20130101; Y02A 20/131 20180101; B01D
11/0492 20130101; B01D 11/0446 20130101; Y02W 10/37 20150501; B01D
11/0446 20130101; B01D 61/005 20130101; C02F 1/38 20130101; B01D
61/002 20130101 |
Class at
Publication: |
210/650 ;
210/670 |
International
Class: |
B01D 61/00 20060101
B01D061/00; B01J 49/00 20060101 B01J049/00 |
Claims
1. A method of recovering a solvent from an osmotic agent solution
stream, comprising the steps of: introducing a polymer having a
cloud point temperature into a first separator comprising the
osmotic agent solution stream; extracting the solvent from the
osmotic agent solution stream, whereby a two-phase mixture
comprising a first phase and a second phase is created, the first
phase comprising the osmotic agent solution stream and the second
phase comprising the polymer with the extracted solvent; separating
the second phase from the first phase; heating the second phase in
a second separator to at least the cloud point temperature of the
polymer to form a polymer rich phase and a solvent rich phase; and
separating the polymer rich phase and solvent rich phase comprising
at least 95 wt % of the extracted solvent.
2. The method of claim 1, further comprising the step of recycling
the polymer rich phase to the first separator.
3. The method of claim 1, further comprising the step of recycling
the first phase to an upstream processing unit.
4. The method of claim 1, further comprising the step of purifying
the extracted solvent.
5. The method of claim 1, wherein the step of separating the second
phase from the first phase comprises centrifugation.
6. The method of claim 1, wherein the step of separating the second
phase from the first phase comprises gravitational settling.
7. The method of claim 1, wherein the step of separating the
polymer rich phase from the solvent rich phase comprises
centrifugation.
8. The method of claim 1, wherein the step of separating the
polymer rich phase from the solvent rich phase comprises
gravitational settling.
9. The method of claim 1, wherein the polymer has a molecular
weight ranging from 500 Daltons to about 10000 Daltons.
10. The method of claim 1, wherein the polymer has a cloud point
temperature ranging from about 5.degree. C. to about 95.degree.
C.
11. A method of recovering water from a feed salt solution,
comprising the steps of: introducing a feed salt solution into an
upstream unit at a first osmotic pressure; introducing an osmotic
agent solution comprising an effective amount of an osmotic agent,
wherein the osmotic agent solution comprises a second osmotic
pressure greater than the first osmotic pressure; inducing a flow
of water from the feed salt solution into the osmotic agent
solution; discharging the feed salt solution from the upstream
unit, the discharged solution having a salt concentration higher
than a salt concentration of the feed salt solution; discharging
the osmotic agent solution from the upstream unit into an
extraction process, whereby a polymer solution having a cloud point
temperature and comprising a polymer selectively absorbs the water
from the osmotic agent solution to create a dehydrated osmotic
agent solution; and heating the polymer solution with the absorbed
water above the cloud point temperature to release the water from
the polymer solution to produce a polymer rich phase and a water
rich phase, the water rich phase comprising at least 95 wt %
water.
12. The method of claim 11, wherein the osmotic agent is magnesium
sulfate.
13. The method of claim 11, further comprising the step of
recycling the dehydrated osmotic agent solution to the upstream
unit in a flow direction countercurrent to the flow of the feed
salt solution.
14. The method of claim 11, wherein the polymer is a co-polymer of
polyethylene oxide and polypropylene oxide.
15. The method of claim 11, further comprising the steps of:
purifying the water rich phase to recover any residual polymer or
residual osmotic agent; and recycling the residual polymer or the
residual osmotic agent to the extraction process.
16. The method of claim 11, wherein the upstream unit comprises
forward osmosis, microfiltration, ultrafiltration, pervaporation,
osmotic distillation, membrane distillation, or any combination
thereof.
17. A method of desalinating a salt water stream, comprising the
steps of: introducing a salt water solution into an upstream unit
at a first osmotic pressure; introducing an osmotic agent solution
comprising an effective amount of an osmotic agent into the
upstream unit, the osmotic agent solution having a second osmotic
pressure greater than the first osmotic pressure; inducing a flow
of water from the salt water solution into the osmotic agent
solution; discharging the salt water solution from the upstream
unit; cooling a first portion of the osmotic agent solution to
crystallize a first portion of the osmotic agent from the osmotic
agent solution; discharging the osmotic agent solution from the
upstream unit into an extraction process, whereby a polymer
solution having a cloud point temperature and comprising a polymer
selectively absorbs the water from the osmotic agent solution; and
heating the polymer solution with the absorbed water to at least
the cloud point temperature to release the water from the polymer
solution and produce a polymer rich phase and a water rich phase
having a composition of at least 95 wt % water.
18. The method of claim 17, further comprising the steps of:
removing a second portion of the osmotic agent from the extraction
process; and recycling the second portion of the osmotic agent into
the upstream unit.
19. The method of claim 17, further comprising the step of
recycling the crystallized portion of the osmotic agent into the
upstream unit.
20. The method of claim 17, wherein the osmotic agent comprises
disodium hydrogen phosphate.
Description
RELATED APPLICATIONS
[0001] The present patent document claims the benefit of the filing
date under 35 U.S.C. .sctn.119(e) of Provisional U.S. Patent
Application Ser. No. 61/148,270, filed Jan. 29, 2009 which is
hereby incorporated by reference.
BACKGROUND
[0002] The present disclosure relates to the separation of solvent
from inorganic and organic solutions, and more particularly to the
removal and purification of solvent from a salt solution
stream.
[0003] The removal of solvents from inorganic or organic solutions
is practiced widely in industry. Typically, the solvent to be
removed is contained within an inorganic or organic solution
stream. Thereafter, the solvent is often subject to purification
processing steps. The purified solvent may be sold as an
intermediate chemical solvent for use in subsequent chemical and
industrial processes. Alternatively, the purified solvent may be
sold as an end-product for consumer use.
[0004] Water is a typical solvent which is often contained in
various inorganic and organic degraded sources. Water contained
within such degraded sources typically is not useable. Accordingly,
the water is generally recovered from such degraded sources to
enable it to be useable and of value in several intermediate and
end-product applications. Currently, the recovery of water from
degraded sources is being employed on an industry-wide basis. As an
example, water is being recovered from brackish or seawater streams
by conventional methods such as evaporation and reverse osmosis.
Water is also being recovered from other degraded water sources,
such as agricultural runoff and industrial waste streams.
[0005] Many of the conventional recovery processes for solvents
such as water are energy intensive, requiring relatively high
temperature and pressure operating levels such that the process
fails to be cost effective. Accordingly, water sources which allow
the recovery of water without energy intensive processes are
preferable. However, the availability of such water sources is
rapidly decreasing. Accordingly, there is a need for a process
which readily allows recovery of solvents such as water from their
respective organic and inorganic streams.
SUMMARY
[0006] In a first aspect, a method of recovering a solvent from an
osmotic agent solution stream is provided. Polymer having a
predetermined cloud point temperature is introduced into a first
separator comprising the osmotic agent solution stream. A two-phase
mixture comprising a first phase and a second phase is created. The
first phase comprises the osmotic agent solution stream and the
second phase comprises the polymer with the extracted solvent.
Solvent is thereby extracted from the osmotic agent solution stream
to the second polymer phase. The second phase is separated from the
first phase. The second phase is heated in a second separator to at
least a cloud point temperature of the polymer to create a polymer
rich phase and a solvent rich phase. The polymer rich phase is
separated from the solvent rich phase comprising at least 95 wt %
of the extracted solvent.
[0007] In a second aspect, a method of recovering water from a feed
salt solution stream is provided. A feed salt solution is
introduced into an upstream unit at a first osmotic pressure. An
osmotic agent solution comprising an effective amount of an osmotic
agent in which the osmotic agent solution comprises a second
osmotic pressure greater than the first osmotic pressure is also
introduced into the upstream unit, thereby inducing a flow of water
from the feed salt solution into the osmotic agent solution. The
feed salt solution is discharged from the upstream unit, such that
the discharged solution has a salt concentration higher than a salt
concentration of the feed salt solution. The osmotic agent solution
is discharged from the upstream unit and enters into an extraction
process, whereby a polymer solution having a predetermined cloud
point temperature and comprising a polymer selectively absorbs the
water from the osmotic agent solution to create a dehydrated
osmotic agent solution. The polymer solution with the absorbed
water is heated above the cloud point temperature to release the
water from the polymer solution and produce a polymer rich phase
and a water-rich phase so that the water rich phase comprises at
least 95 wt % water.
[0008] In a third aspect, a method of desalinating a salt water
stream is provided. A salt water solution is introduced into an
upstream unit at a first osmotic pressure. An osmotic agent
solution comprising an effective amount of an osmotic agent is
introduced into the upstream unit. The osmotic agent solution has a
second osmotic pressure greater than the first osmotic pressure. A
flow of water is induced from the salt water solution into the
osmotic agent solution. The salt water solution is discharged from
the upstream unit. A first portion of the osmotic agent solution is
cooled to crystallize a first portion of the osmotic agent from the
osmotic agent solution. The osmotic agent solution is discharged
from the upstream unit into an extraction process, whereby a
polymer solution having a predetermined cloud point temperature
selectively absorbs the water from the osmotic agent solution. The
polymer solution is heated with the absorbed water to at least the
cloud point temperature to release the water from the polymer
solution and produce a polymer rich phase and a water rich phase
having a composition of at least 95 wt % water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows a process schematic of an embodiment of a
solvent extraction process.
[0010] FIG. 2 shows a process schematic of an embodiment of a
desalination process.
DETAILED DESCRIPTION
[0011] The relationship and functioning of the various elements of
this invention are better understood by the following detailed
description. However, the embodiments of this invention as
described below are by way of example only. Unless otherwise
specified, all percentages expressed herein are weight percentages
based on the whole mixture.
[0012] An exemplary solvent recovery process 100 for capturing
solvent 111 from a feed stream will now be described in conjunction
with FIG. 1. FIG. 1 shows a feed stream 110 comprising a solvent
111 and solute. The solvent 111 may be any type of inorganic or
organic solvent. The solvent may be present in a matrix that is a
gas, vapor, liquid, or solid. Generally speaking, the solvent 111
may be recovered as a purified product stream 158 from feed stream
110, and the solute may exit an upstream processing module as
concentrated stream 120.
[0013] In one embodiment, the feed stream 110 may be a liquid.
Referring to FIG. 1, the feed stream 110 enters processing
equipment which includes a semi-permeable membrane 112. The
semi-permeable membrane includes pores which are designed to have a
size that is large enough for solvent to flow through but too small
for the solute to pass through. In other words, the semi-permeable
membrane is impermeable to the solute but allows for the flow of
the solvent 111.
[0014] An upstream processing unit may employ any of numerous types
of semi-selective processes to allow solvent 111 to pass to the
osmotic agent stream. Examples of semi-selective processes to allow
solvent 111 to pass across the membrane 112, include, but are not
limited to, microfiltration, ultrafiltration, nanofiltration,
forward osmosis, pervaporation, osmotic distillation, membrane
distillation, and any combination of the above. In other cases
where the solvent is within a solid matrix, the flow of the solvent
can be induced by other processes, such as, for example, immersion
or leaching by an osmotic agent. In these cases, the
semipermeability may be provided by the composition of the solid
matrix itself. An example of such a process may be osmotic
dehydration of vegetables or fruits where the naturally present
cell walls present a semi-permeable barrier. In cases where the
matrix is a present in a gaseous or vaporous form, the solvent can
be induced to flow from the matrix into a receiving osmotic agent
solution by vapor pressure differences or by absorption. In a
preferred embodiment, a forward osmosis unit 130 is used as the
means to induce solvent flow across the semi-permeable membrane, as
indicated by the arrow across the membrane 112 within osmosis unit
shown in FIG. 1.
[0015] The forward osmosis process utilizes a semi-permeable
membrane to cause separation of the solvent from the dissolved
solutes in the feed stream 110. The feed stream 110 enters a first
inlet of the forward osmosis unit 130. An osmotic agent stream 140
enters a second inlet of the forward osmosis unit. A semi-permeable
membrane within the forward osmosis unit serves as a barrier
between the streams 110 and 140. The streams 140 and 110 are
preferably flowing in opposite directions in a countercurrent flow
configuration. Countercurrent flows of streams 110 and 140 enable
the most concentrated feed stream 120 to contact the most
concentrated osmotic agent stream 140 to ensure solvent 111 to flow
due to the osmotic pressure gradient, which is defined as the
difference in osmotic pressures on the two sides of the
semi-permeable membrane.
[0016] The osmotic agent stream 140 comprises a selected osmotic
agent in an effective amount so as to have a higher osmotic
pressure than the corresponding osmotic pressure of the feed stream
110 at all locations within unit 130 (i.e., osmotic pressure of
stream 140 is greater than that of stream 120 and the osmotic
pressure of stream 145 is greater than that of stream 110).
"Effective amount" as used herein refers to selecting a
concentration of the selected osmotic agent to create the necessary
flow of solvent 111 from the feed stream 110 to the osmotic agent
stream 140. Generally speaking, the lower the concentration of the
osmotic agent, the lower the osmotic pressure of the stream 140.
Accordingly, an effective amount of osmotic agent is dissolved into
the solution of the osmotic agent stream 140 until the osmotic
pressure of stream 140 is higher than that of feed stream 110 to
create an osmotic pressure gradient across the membrane 112. In
other words, the addition of the osmotic agent decreases the
chemical potential of the corresponding solvent (i.e., the activity
of the solvent) on the side of the membrane 112 containing the
osmotic agent stream 140 until it is below that of the feed stream
110, thereby creating a chemical potential gradient. Such a
gradient induces the flow of solvent across the semi-permeable
membrane from the feed stream 110 into the osmotic agent stream
140. The maximum effective amount of the selected osmotic agent
that can be added to the osmotic agent stream 140 may be limited by
the solubility limit of the particular osmotic agent in the
corresponding solvent of the osmotic agent stream 140 for a given
temperature of the stream 140.
[0017] As the feed stream 110 and the osmotic agent stream 140 flow
countercurrently along the length of the forward osmosis unit,
solvent 111 flows via forward osmosis from the feed stream 110 into
the osmotic agent stream 140, as indicated by the arrow within unit
130. The flow of solvent continues so long as the osmotic pressure
gradient exists between the streams 110 and 140 at all locations
within unit 130. The osmotic pressure gradient and resultant flow
of solvent 111 enables dehydration of the feed stream 110 such that
concentration of the solute in the feed stream increases. The flow
of solvent 111 into the osmotic agent stream 140 increases the
concentration of solute in feed stream 110. Feed stream 110 exits
forward osmosis unit 130 as concentrated solute stream 120. Osmotic
agent stream 140 exits the forward osmosis unit 130 as stream 145,
which is now diluted with the solvent 111. The extent to which
stream 120 becomes concentrated with solute may be governed by the
amount of solvent 111 that flows from feed stream 110 to osmotic
agent stream 140. The amount of solvent 111 that flows into stream
140 is driven by the osmotic pressure gradient, which is determined
by how much osmotic agent can be dissolved into its solution (i.e.,
the solubility of the osmotic agent in its respective solvent). In
other words, a higher concentration of osmotic agent within stream
140 will induce a larger amount of solvent 111 flow from feed
stream 110 to osmotic agent stream 140.
[0018] The next stage of the solvent recovery process involves
separating the solvent 111 from the osmotic agent contained in
stream 145. A polymeric stream 160 is introduced into stream 145.
The resultant mixture 146 thereafter flows into a separator 150.
The polymer stream 160 has the ability to extract the solvent 111
from stream 145. Sufficient residence time is provided to allow a
two-phase mixture to develop in which the polymer extracts the
solvent 111. A polymer rich phase and an osmotic agent rich phase
are created. The extent of the extraction of solvent 111 may be
determined from a ternary phase diagram of the osmotic agent,
solvent 111, and polymer components.
[0019] The osmotic agent rich phase is recycled back to forward
osmosis unit 130. Preferably, trace amounts or none of the polymer
is recycled back with the osmotic agent rich phase, as introduction
of substantial amounts of the polymer within the osmotic agent may
tend to increase viscosity or interfere with operational
efficiency. The polymer rich phase with extracted solvent 111
(i.e., the polymer-solvent phase) exits the separator as stream
151. Preferably, trace amounts or none of the osmotic agent is
extracted into the polymer rich phase, as this may increase
subsequent solvent purification costs.
[0020] The polymer rich-solvent mixture exits the separator as
stream 151. The polymer-solvent mixture 151 is heated in heater 156
at least to its predetermined cloud point temperature to release
the solvent 111. Cloud point temperature can be determined by ASTM
standard D2024-65 (2003).
[0021] The polymer exits separator 153 as stream 155 and thereafter
may be recycled back as stream 155 and re-introduced into stream
145 after blending with stream 159 labeled concentrated residual
polymer. The released solvent 111 is separated from the polymer in
separator 153 and then exits separator 153 as stream 157. The
released solvent 111 may then undergo one or more purification
steps in downstream processing. FIG. 1 shows that the released
solvent stream 157 may be purified in a purification or polishing
step 168, in which any residual polymer and any residual osmotic
agent from upstream is removed. The purification/polishing step 168
may be a reverse osmosis step in which external pressure is used to
drive the solvent 111 across a semi-permeable membrane 162 to the
other side of the membrane while the residual polymer/trace salt is
retained on the inlet side of the membrane. With the residual
polymer/trace salt isolated from the solvent 111, the residual
polymer/trace salt may be recycled back as stream 159, combined
with stream 155 and re-introduced into stream 145 to selectively
extract additional solvent from additional osmotic agent stream 145
that is exiting forward osmosis unit 130.
[0022] Other polishing steps for recovering residual polymer may be
utilized, including for example, oxidation, adsorption, absorption,
ion exchange, membrane distillation, ultrafiltration,
microfiltration, nanofiltration, foam fractionation, dissolved air
flotation, coacervation, precipitation, crystallization,
chromatographic separations or solvent extraction with a water
immiscible solvent, electrodialysis, capacitive deionization,
combination thereof, or other means of separations as readily
apparent to one of ordinary skill in the art to remove/capture any
residual polymer or trace salt. Furthermore, operations such as
sequential cloud point extractions, or staged cloud point
extractions in combination with phase separations that may result
in either increased solvent recovery or lower processing costs are
clearly contemplated as part of this disclosure.
[0023] It is contemplated that the above described recovery process
may occur on a continuous basis for a given uninterrupted time
period at predetermined mass flow rates. Alternatively, the
recovery process may occur on a batch basis comprising discrete
processing stages.
[0024] It is also contemplated that the process can be carried out
in stages. In one example, the exiting process stream 145 is
initially contacted with a polymer stream followed by separator 150
that results in streams 151 and 140. In a subsequent step, stream
140 can be further contacted with the polymer to result in a second
fractionation. Such steps have the advantage of producing a
concentrated osmotic agent for subsequent use in forward osmosis
unit 130 while allowing for additional solvent recovery.
[0025] Numerous types of polymers and co-polymers (linear,
branched, dendrimers, etc.) for extraction of the solvent can be
used either singly or in combination, including for example,
ethoxy(hydroxyethyl) cellulose, polyvinyl alcohol,
poly(n-vinylcaprolactam), polyethylene glycol, polypropylene oxide,
copolymers of polyethylene oxide and polypropylene oxide, polymers
of alkylene oxides, Triton.RTM. X-114, polyvinyl alcohol acetate,
ethoxylated cellulose, acrylate-acrylic copolymers, phosphorus
containing polyolefins, partially substituted ethyl and methyl
cellulose ethers, copolymers of vinyl alcohol and methyl vinyl
ketone, copolymers of maleic acid diesters of propylene glycol and
butyl alcohol with maleic acid diesters of propylene glycol and
octyl alcohol, copolymers of propylene glycol methacrylate and
methyl methacrylate, copolymers of vinyl alcohol or maleic acid
diesters of propylene glycol and butyl alcohol, copolymers of
propylene glycol methacrylate or methylvinylether and methallyl
alcohol or methylvinyl ketone or maleic acid diesters of propylene
glycol and octyl alcohol or methyl methacrylate or acrylonitrile or
styrene, copolymers of vinyl pyrollidone, acrylamide,
ethyleneamine, hexamethyleneimine, vinyl carbazole and vinyl
pyridine or copolymers of methallyl alcohol or methyl vinyl ketone
or maleic acid diester of propylene glycol and octyl alcohol or
methyl methacrylate or acrylonitrile or styrene; polyethylene oxide
polybutyleneoxide, polyethylene oxide-polytetramethyleneether,
polyvinylpyrrolidone, methoxypolyethyleneglycol, polyglycol
terpolymers such as U-11755.RTM., vinylpyrrolidone/vinyl acetate
copolymer and others as elucidated in U.S. Pat. No. 3,386,912.
Additionally, the polymers disclosed in U.S. Pat. Nos. 3,438,893,
3,234,125, 3,234,126, 3,441,501, 3,451,926, 5,354,835 may be
utilized and are hereby incorporated by reference. Other suitable
polymers can be found in compilations such as CRC handbook of
thermodynamics data of aqueous polymer solutions (2004) by C.
Wohlfarth: CRC Press, Boca Raton, Fla., USA. The above described
polymers may be fluid-like in structure. Alternatively, the above
described polymers may be synthesized to create a relatively more
rigid structure by cross-linking so as to create a resin or film
type structure. One example of a suitable cross linked polymer is
N-vinyl-2-ethyl-imidazole, which is cross-linked with
dibromo-p-xylene.
[0026] Preferably, the above listed polymers will have a molecular
weight between 500 and 10,000 Daltons. Such a range of molecular
weight maintains the viscosity at a relatively low level such that
handling and transport difficulties are avoided. Additionally,
increasing the molecular weight significantly beyond 10,000 Daltons
may reduce the osmotic pressure of osmotic agent stream 140 if any
portion of the polymer is recycled back to the forward osmosis unit
130. The reduction of osmotic pressure will decrease the osmotic
pressure gradient that induces solvent flow from the feed stream
110 to the osmotic agent stream 140.
[0027] Numerous types of osmotic agents are contemplated for use
either singly or in combination. For example, the osmotic agent may
be an ionized salt, ionic polymer, ionic liquids, nonionic polymer,
or organic compounds. Suitable examples of salts include but are
not limited to sodium hydroxide, sodium carbonate, sodium
silicates, disodium sulfate, trisodium phosphate, sodium formate,
sodium succinate, sodium tartrate, sodium citrate, dilithium
sulfate, ammonium sulfate, ammonium carbonate, ammonium carbamate,
zinc sulfate, copper sulfate, iron sulfate, magnesium sulfate,
aluminum sulfate, disodium monohydrogenphosphate, monosodium
dihydrogenphosphate, tripotassium phosphate, dipotassium carbonate,
manganese sulfate, and potassium citrate. Suitable examples of
ionic polymers include but are not limited to polyacrylic acid, low
molecular weight poly(ethylenesulfonic) sodium salt,
polymethylacrylic sodium salt, and various copolymers. Suitable
examples of nonionic polymers include but are not limited to
dextran; dimer, trimers, etc. of sugars including for example
glucose, fructose and the like. Suitable examples of organic
compounds include, but are not limited to glycerol, ethylene
glycol, diethylene glycol, triethanolamine, ethanol, propanol,
acetone, and diethylether. Preferably the osmotic agent is disodium
hydrogen phosphate or magnesium sulfate.
[0028] Numerous types of feed streams may be processed, including
solids, gases, and liquids, in which the solute in the feed stream
may be present in any concentration. For example, the feed stream
may be seawater comprising NaCl as the solute. Alternatively, the
feed stream may comprise municipal water or treatment plant
effluent comprising various contaminant solutes to be separated
from the water, or process effluents such as cooling tower, boiler
blowdown, or ion exchange rinses and regenerant solution. The feed
streams listed here are illustrative by way of example and are not
intended to be limiting.
[0029] In a preferred embodiment, the feed stream to be processed
is seawater, and the seawater may comprise about 4 wt % or less
NaCl of the total mixture. The salt may be separated from the water
in a desalination process similar to the solvent recovery process
explained above. The seawater feed stream is dehydrated utilizing a
forward osmosis unit into which an osmotic agent stream having a
predetermined concentration of osmotic agent salt is introduced
therein.
[0030] Similar to the solvent recovery process described above, the
pore size of the semi-permeable membrane is sufficiently large to
enable the solvent water to flow from the seawater feed stream into
the osmotic agent stream. However, the pore size is too small to
allow the NaCl to flow through. The net flow of water into the
osmotic agent stream from the seawater feed stream dilutes the
osmotic agent stream while increasing the concentration of the NaCl
in the seawater feed stream. Accordingly, stream 120 exits the
forward osmosis unit dehydrated and increasingly concentrated in
NaCl while stream 145 exits forward osmosis unit diluted with the
water 111 such that concentration of the osmotic agent salt has
decreased.
[0031] The recovery of the water from the osmotic agent stream 145
involves introducing polymer stream 160 into the osmotic agent
stream to selectively extract the water from stream 145. The
polymer utilized in the extraction of the desalination process may
be a copolymer. The above described copolymers may be random, in
which the polymerization of each of the monomers occurs in a random
manner. Alternatively, the above described copolymers may be a
block structure in which polymerization of the first monomer
occurs, thereafter followed by polymerization of the second monomer
to create a resultant structure having defined and discrete domains
of each of the polymerized chains within the copolymer.
[0032] The copolymer in the desalination process preferably has a
hydrophilic polymeric region which binds to the water to facilitate
extraction of the water from the osmotic agent solution stream 145
that exits the forward osmosis unit. The copolymer preferably has a
hydrophobic polymeric region that is relatively weakly bound to the
water, thereby facilitating separation of the polymer from the
water at a lower temperature compared to a polymer containing only
hydrophilic regions. The combination of hydrophilic and hydrophobic
regions affords an overall copolymer structure having a lower cloud
point temperature relative to the cloud point temperature of a
polymer that has only hydrophilic regions. Unlike a copolymer
having hydrophobic and hydrophilic regions, a polymer with only a
hydrophilic region requires more energy to break the hydrogen bonds
and therefore will possess a higher cloud point temperature.
[0033] In a preferred embodiment, a random copolymer comprising
polyethylene oxide and polypropylene oxide (PEO-PPO) may be used.
The PEO-PPO copolymer mixture can be commercially obtained from DOW
Chemical as UCON.RTM. 50 HB-660. Polymers of similar composition
can also be obtained commercially from many other chemical
producers. UCON.RTM. 50 HB-660 is substantially nontoxic such that
residual amounts of the polymers in water 111 can exit stream 157
without posing any health risk. Introduction of the PEO-PPO random
copolymer into stream 145 (i.e., the osmotic agent stream 140 which
exits the forward osmosis unit and which is now diluted with the
solvent water 111) enables water to be extracted from stream 145,
thereby creating a polymer-water rich phase and an osmotic agent
rich phase. Subsequent heating of the copolymer of PEO-PPO and
water 111 mixture slightly beyond its cloud point temperature
releases the extracted water from the PEO-PPO copolymer.
Specifically, this particular copolymer of PEO-PPO will release
water when the polymer rich phase mixture 151 is heated slightly
above its cloud point temperature a range between about 60.degree.
C. and about 80.degree. C.
Laboratory Procedure
[0034] Known quantities of aqueous solutions of MgSO.sub.4
heptahydrate were mixed with known quantities of 100% UCON.RTM.
50-HB-660 to obtain mixtures of varying salt and polymer
concentrations. The resulting mixtures were allowed to separate to
produce a polymer rich phase and a salt rich phase. Separation was
carried out either under gravity or under a centrifugal field. The
quantities of the polymer rich phase and the salt rich phase were
measured. The phases were analyzed for their respective MgSO.sub.4
and UCON.RTM. 50-HB-660 contents by ICP-MS and HPLC Chromatography
methods as known in the art. The composition data along with phase
quantity allowed complete mass balances (shown below) to be
constructed for the mixture compositions. The polymer rich phase
was then subject to heating above the cloud point to obtain a
polymer rich phase and a substantially water rich phase with small
residual amounts of polymer and salt. The quantities of the water
rich phase and polymer rich phases were determined by measurement
and their phase compositions analyzed as previously mentioned
above. The temperature of phase separation was varied to determine
its effect on phase composition and quantity.
[0035] Separately, an experiment was carried out in which a water
rich solvent phase with varying amounts of MgSO.sub.4 and polymer
was subject to purification by reverse osmosis in a conventional
stirred cell module at pressures of about 400 psi. This experiment
enabled estimating resulting water quality and the amount of
recovery.
[0036] Data from the above experiments were then checked for data
quality through mass balance closures. The resulting data set
allowed the construction of flow sheets that represent multiple
cycles of water extraction and purification as represented in
Examples 1-6. The Examples 1-6 will be discussed with reference to
FIG. 2, which represents a flow sheet for a water recovery and
purification process 200 from a saline water stream using an
osmotic agent solution.
Example 1
[0037] Saline feed stream 210 entered forward osmosis unit 230
having an incoming salt content less than or equal to typical
seawater. Stream 240 and 245 represented osmotic agent solutions
entering and leaving the forward osmosis unit 230, respectively.
The most concentrated osmotic agent stream 240 extracted water from
the most concentrated seawater stream 220 while the diluted osmotic
agent stream 245 extracted water from the less concentrated saline
stream 210. Stream 245 was mixed with a stream 260 to produce
stream 246. Stream 246 was thereafter introduced into the first
separator 250 to allow separation of the polymer-water rich phase
from the osmotic agent rich phase by gravitational settling. The
compositional and mass balance for the process assuming a mass of
200 grams for stream 246 was determined and is shown below in Table
1. In particular, FIG. 2 and Table 1 show that upon separation of
the phases within the first separator 250, 172 grams of the
concentrated osmotic agent stream 240 was available for recycling
back to the forward osmosis unit 230 to induce additional water
flow across the membrane 212 from saline feed stream 210. Stream
240 had composition of about 22.67% MgSO.sub.4, 76.82% water, and
0.51% polymer. Stream 252 exited the first separator 250 as the
polymer-rich phase. The stream 252 was comprised of 28 grams of
polymer rich phase having a composition of about 69% UCON.RTM.
50-HB-660 and 31% water. Favorable extraction occurred. In other
words, upon extraction of the water from the osmotic agent, a
majority of the MgSO.sub.4 was able to be recycled from the first
separator back to the forward osmosis unit, and a majority of the
UCON.RTM. 50-HB-660 polymer was separated from the osmotic salt
agent solution stream 240. Accordingly, MgSO.sub.4 and UCON.RTM.
50-HB-660 losses were relatively low. In particular, about 0.01
grams of the MgSO.sub.4 salt was extracted with the water into the
polymer-rich phase, which represents about 0.03% weight loss (i.e.,
the amount of MgSO.sub.4 which was extracted with the water into
the polymer-rich phase in the first separator) based on the initial
39 grams of MgSO.sub.4 contained in stream 246. It was observed
that osmotic agent stream 240 contained 0.51% UCON.RTM. 50-HB-660.
In other words, about 0.88 grams of the UCON.RTM. 50-HB-660 polymer
was recycled back into the forward osmosis unit, as shown in Table
1. About 95.6% of the polymer was favorably separated from the
osmotic agent solution and subject to further downstream
processing.
[0038] The water recovery and purification process subsequently
involved separation of the desalinated water from the UCON.RTM.
50-HB-660 polymer in stream 252. Stream 252 entered a heat
exchanger 256 as shown in FIG. 2. The heat exchanger raised the
temperature of stream 252 to about 80.degree. C., which was above
the cloud point temperature of the UCON.RTM. 50-HB-660. Heating the
stream 252 to about 80.degree. C. resulted in formation of a
polymer-rich phase and a water-rich phase. The steam 252 exited the
heat exchanger and thereafter was introduced into a second
separator 253 to allow separation of the polymer-rich phase from
the water-rich phase. Separation of the phases was achieved by
gravitational settling. The separated phases exited the second
separator 253 as a water-rich phase, which is designated stream 257
in FIG. 2, and a polymer-rich phase, which is designated as stream
255 in FIG. 2. The polymer-rich stream 255 was mixed with stream
259 and after adjusting for the minor MgSO.sub.4 and the polymer
losses, stream 260 was recycled back to the diluted osmotic agent
stream 245, as shown in FIG. 2 for further extraction of water.
Stream 257 had a water purity of about 99% with trace amounts of
MgSO.sub.4 and polymer as shown in Table 1.
[0039] Stream 257 was further treated in a purification device to
achieve further purification for various end uses and to remove
trace amounts of MgSO.sub.4 and polymer. The purification device
261 was a reverse osmosis membrane 262 which retained all of the
residual salt and polymer, thereby producing a purified water
stream 258. The purified water exited the device as stream 258. The
trace amounts of MgSO.sub.4 and polymer exited the device as stream
259. The stream 259 was mixed with the stream 255. After adjusting
for the minor MgSO.sub.4 and the polymer losses, the final stream
260 was recycled back to the diluted osmotic agent stream 245 to
extract more water, as shown in FIG. 2.
[0040] Two ratios were considered to evaluate the performance of
the desalination process. The mass ratio of stream 257 to 252 was
determined to be 0.199. The ratio provided an indicator of the
effectiveness of the separation of the polymer from water by
quantifying the amount of the water phase that was extracted from
the polymer-rich stream 252. The mass ratio of stream 252 to stream
246 was determined to be 0.138. This ratio provided an indicator of
system volume required to produce a predetermined amount of product
water in stream 252 from stream 246 (i.e. the stream resulting from
introducing polymer stream 260 into diluted osmotic agent stream
245).
TABLE-US-00001 TABLE 1 Streams 246 240 245 252 255 257 258 259 260
Total 200.00 172.29 177.29 27.71 22.20 5.52 5.00 0.52 22.71 grams
MgSO.sub.4 19.53 22.67 22.03 0.04 0.00 0.22 0.00 2.34 0.05 (wt %)
UCON- 10.00 0.51 0.50 69.00 85.95 0.80 0.00 8.52 84.19 660 (wt %)
Water 70.47 76.82 77.47 30.96 14.05 98.98 100.00 89.13 15.76 (wt
%)
Example 2
Effect of Lower Polymer Concentration
[0041] The water recovery and purification process for desalinating
seawater as described in Example 1 was simulated for a lower
concentration of the UCON.RTM. 50-HB-660 polymer in stream 246. The
UCON.RTM. 50-HB-660 polymer concentration in stream 246 was reduced
from 10% in Example 1 to 5%. The compositional and mass balance
results that were achieved for this modified process are shown in
Table 2 below.
TABLE-US-00002 TABLE 2 Streams 246 240 245 252 255 257 258 259 260
Total 200.00 184.51 188.51 15.49 11.10 4.40 4.00 0.40 11.49 grams
MgSO.sub.4 19.53 21.17 20.72 0.04 0.00 0.15 0.00 1.67 0.05 (wt %)
UCON- 5.00 0.21 0.21 62.00 85.84 1.80 0.00 20.00 83.58 660 (wt %)
Water 75.47 78.61 79.07 37.96 14.16 98.05 100.00 78.33 16.37 (wt
%)
[0042] As can be seen in Table 2, the mass ratio of stream 257 to
stream 252 was determined to be 0.284. Although this ratio was
higher than that of Example 1, the total amount of desalinated
water extracted was less compared to Example 1. Reducing the
polymer concentration in stream 246 to 5% reduced stream 257 (which
is representative of the amount of the water phase extracted from
stream 246) from 5.52 grams (Table 1) to 4.40 grams. Additionally,
the purity of water in stream 257 was reduced from 98.98% to
98.05%. Accordingly, the lower concentration of polymer produced a
relatively poorer quality of product water compared to Example
1.
Example 3
Effect of Centrifugation
[0043] The water recovery and purification process for desalinating
seawater as described in Example 1 was repeated utilizing
centrifugation rather than gravitational settling as the means of
achieving separation of phases. Phase separation of stream 246 was
achieved by centrifugation. In particular, centrifugation was
utilized for separating the polymer-rich phase from the osmotic
agent rich phase of stream 246. A centrifugal force of about 1744 g
was applied to stream 246 for 5 minutes. The compositional and mass
balance results that were achieved for this modified process are
shown in Table 3 below.
TABLE-US-00003 TABLE 3 Streams 246 240 245 252 255 257 258 259 260
Total 200.00 168.64 176.64 31.36 22.91 8.45 8.00 0.45 23.36 grams
MgSO.sub.4 19.53 23.16 22.11 0.04 0.00 0.16 0.00 3.02 0.05 (wt %)
UCON- 10.00 0.15 0.14 63.00 86.05 0.50 0.00 9.43 84.58 660 (wt %)
Water 70.47 76.70 77.75 36.96 13.96 99.34 100.00 87.55 15.37 (wt
%)
[0044] The centrifugation reduced the time required for separation
of the phases in stream 246. The centrifugation also increased the
mass ratio of stream 257 to stream 252 from 0.199 in Example 1 to
0.269 as determined from Table 3. A comparison of Table 1 and 3
shows that the amount of water rich phase, which is designated as
stream 257, was over 50% greater than that of Example 1.
Additionally, the purity and amount of water product (stream 257)
was higher compared to Example 1. The mass ratio of stream 252 to
stream 246 was about 14% higher than that of Example 1, which
indicates a lower system volume was needed to produce the desired
amount of purified desalinated water.
Example 4
Effect of Lower Temperature During Formation and Separation of Two
Phase Mixture
[0045] The water recovery and purification process for desalinating
seawater as described in Example 3 was repeated utilizing a lower
temperature during separation of the polymer phase (stream 255
exiting separator 253) from the water-rich phase (stream 257
exiting separator 253). The temperature during this separation was
lowered from 80.degree. C. to 60.degree. C. Centrifugation as
described in Example 3 (1744 g for 5 minutes) was used in place of
gravitational settling. The compositional and mass balance results
that were achieved for this modified process are shown in Table 4
below.
TABLE-US-00004 TABLE 4 Streams 246 240 245 252 255 257 258 259 260
Total 200.00 170.19 173.19 29.82 26.44 3.37 3.00 0.37 26.82 grams
MgSO.sub.4 19.53 22.95 22.55 0.05 0.00 0.45 0.00 4.01 0.06 (wt %)
UCON- 10.00 0.19 0.19 66.00 73.99 3.40 0.00 30.63 73.38 660 (wt %)
Water 70.47 76.86 77.26 33.95 26.01 96.16 100.00 65.36 26.56 (wt
%)
[0046] The lower temperature of separation resulted in a lower mass
ratio of stream 257 to stream 252 of 0.113 compared to the ratio of
0.269 attained in Example 3. Additionally, product stream 257
contained 96.16% water purity compared to 99.34% water purity
attained in Example 3. Accordingly, the amount of water and the
purity of the water were less compared to Example 3.
Example 5
[0047] The water recovery and purification process for desalinating
as described in Example 1 was repeated with the addition of a small
quantity of sodium chloride in the osmotic agent stream to simulate
nonideality of the semi-permeable membrane. As can be seen in Table
5, the process results are comparable to those shown in Example 1
indicating substantial robustness of the process.
TABLE-US-00005 TABLE 5 Streams 246 240 245 252 255 257 258 259 260
Total 200.02 172.74 177.74 27.28 21.74 5.54 5.00 0.54 22.28 grams
MgSO.sub.4 19.53 22.60 21.97 0.10 0.00 0.51 0.00 5.22 0.12 (wt %)
NaCl 0.35 0.40 0.39 0.04 0.00 0.19 0.00 1.95 0.05 (%) UCON- 10.00
0.05 0.05 73.00 91.44 0.65 0.00 6.66 89.38 660 (wt %) Water 70.11
76.94 77.59 26.86 8.56 98.65 100.00 86.17 10.45 (wt %)
Example 6
[0048] The water recovery and purification process for desalinating
was repeated with disodium hydrogen phosphate as the osmotic agent
as shown in Table 6. It can again be seen that water of adequate
quality can be obtained through the addition of polymer to the
osmotic agent.
TABLE-US-00006 TABLE 6 Streams 246 240 245 252 255 257 258 259 260
Total 200.37 146.12 151.43 54.25 48.35 5.90 5.31 0.59 48.94 grams
Na.sub.2HPO.sub.4 11.98 16.42 15.84 0.03 0.00 0.24 0.00 2.40 0.03
(wt %) UCON- 20.14 0.00 0.00 74.40 83.36 1.00 0.00 10.00 82.47 660
(wt %) Water 67.88 83.58 84.16 25.57 16.64 98.76 100.00 87.60 17.49
(wt %)
[0049] The above examples 1-6 disclose that the extraction of water
by the polymer can occur at ambient temperature and pressure
operating conditions, with the exception of the separation step
requiring heating of the UCON.RTM. 50-HB-660 polymer at least to
its cloud point temperature. Waste heat from a power plant, solar
energy or any other suitable source may be used to supply the heat
energy requirements when heating UCON.RTM. 50-HB-660 polymer to its
cloud point temperature. Preferably, the UCON.RTM. 50-HB-660 is
heated to a maximum of about 25.degree. C. above cloud point
temperature to release the captured water, in the interests of
minimizing the input energy requirement. However, heating beyond
such a range is contemplated within the scope of this embodiment.
Further release of water may be accomplished by heating beyond
25.degree. C. above the open cloud point temperature. The upper
limit of this range may be governed by numerous factors, including
the temperature at which decomposition or changes to the chemistry
of the polymer may occur. Preferably, the UCON.RTM. 50-HB-660 is
heated to 24.degree. C. above its cloud point temperature to
release the captured water. The cloud point of 1% UCON.RTM.
50-HB-660 in water is about 56.degree. C. In one example, the
UCON.RTM. 50-HB-660 may be heated to a cloud point temperature
ranging from about 5.degree. C. to about 95.degree. C. The exact
cloud point temperature will be primarily dependent upon the
polymer used.
[0050] The amount of waste heat required may be significantly less
than the energy required for conventional desalination processes.
Accordingly, the disclosed process may significantly reduce the
costs associated with energy intensive desalination processes such
as distillation, which typically require higher temperatures and
pressures and often necessitate phase change of the material being
processed. Additionally, the disclosed process does not require
chemical precipitants as are commonly used in conventional
processes. Rather, the materials used in the disclosed process may
be reusable. The polymers may be recycled back to selectively
extract additional water from the diluted osmotic agent stream 245.
The osmotic agent salts may be recycled back to the forward osmosis
unit to induce additional water 211 flow via forward osmosis.
Furthermore, unlike conventional desalination processes, the NaCl
concentration in stream 220 may be concentrated to greater than
10%. The disclosed desalination process is sufficiently robust such
that it can work with any incoming salt concentration in the
seawater feed stream 210 provided it is lower in osmotic
concentration relative to stream 245.
[0051] Examples 1-6 indicate that the concentration of osmotic
agent salt MgSO.sub.4 was slightly over 20% in osmotic agent stream
240. Such a high concentration of the MgSO.sub.4 enables the NaCl
in solute stream 220 to be as concentrated as 8%. Generally
speaking, the desalination process will preferably utilize the
highest amount of MgSO.sub.4 possible in stream 240 to create the
lowest water activity (i.e. the highest osmotic pressure) and
therefore the maximum driving force to induce the flow of water
from the seawater feed stream 210 to the osmotic agent stream
240.
[0052] In an alternative embodiment, an alternative osmotic salt
agent capable of further dewatering seawater feed stream 210 may be
provided such that solute stream 220 may comprise up to about 15%
NaCl. One suitable osmotic agent salt that may accomplish this is
disodium hydrogen phosphate, which possesses higher water
solubility than MgSO.sub.4 at room temperature. The higher
solubility of disodium hydrogen phosphate enables stream 240 to
exert a higher osmotic pressure, thereby inducing a greater flow of
water 111 such that solute stream 220 can be concentrated up to
about 15% NaCl. Up to about 40% of the disodium hydrogen phosphate
can be utilized at about 40.degree. C.
[0053] As before, the osmotic agent salt solution stream 240 exits
the forward osmosis unit 230 as stream 245, which is now diluted
with a higher amount of water than possible with MgSO.sub.4. Stream
245 may be cooled to form crystals of disodium hydrogen phosphate
to drive at least a portion of the disodium hydrogen phosphate out
of solution of stream 245 to reduce the concentration of salt in
the aqueous phase to about 7-10%. The remaining disodium hydrogen
phosphate solution of the stream 245 may then be extracted to
obtain desalinated water by using a polymer extraction process,
such as the process explained above in accordance with FIGS. 1 and
2 and Examples 1-6.
[0054] It should be appreciated that the above described methods
and compositions are capable of being incorporated in the form of a
variety of embodiments, only a few of which have been illustrated
and described above. The invention may be embodied in other forms
without departing from its spirit or essential characteristics.
However, the described embodiments are to be considered in all
respects only as illustrative and not restrictive, and the scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *